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MicrophoneRelated Patent Categories: Electrical Audio Signal Processing Systems And Devices, Circuitry Combined With Specific Type Microphone Or LoudspeakerMicrophone description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060239475, Microphone. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to a capacitor microphone capable of providing favorable directivity and frequency characteristic. [0003] 2. Description of the Related Art [0004] An output voltage of a capacitor microphone unit is proportional to a displacement of a vibrating membrane. If the capacitor microphone unit is configured as a non-directional microphone unit, the capacitor microphone unit has no frequency dependence at a frequency lower than a resonance point of a vibrating system. However, once directivity is provided for the capacitor microphone unit, an electromotive force applied to the vibrating membrane has frequency dependence. [0005] FIG. 8 shows the most standard configuration of a unidirectional microphone unit. FIG. 8 shows an internal structure of the directional microphone unit. In a cylindrical outer casing 11, a case 12 having a rear plate 12R on one end of a cylindrical body in an axial direction is housed. On the other end of the case 12 in the axial direction, a diaphragm (for example, a thin vibrating membrane; a vibrating section) 13 for closing the open end of the case 12 is provided. [0006] At the location separated from the diaphragm 13 by a predetermined distance toward the rear plate 12R, a back plate 14 including a plurality of holes perforated therethrough is provided. In the approximate center of the back plate 14 in a radial direction, an electrode bar 14a having a predetermined diameter is formed. The electrode bar 14a is provided to extend toward the rear plate 12R so that its end penetrates through the rear plate 12R to form an electrically-conductive terminal 14aa. [0007] A plurality of through holes 15 are provided in the rear plate 12R. An acoustic resistor 16 made of, for example, cloth is provided on an end of each of the through holes 15, the end being on the outer side of the rear plate 12R. A thin fluid layer 17 is formed by a gap between the diaphragm 13 and the back plate 14. An air resistance of the thin fluid layer 17 is set high enough to prevent a resonance of the diaphragm 13 at a high frequency and not to greatly affect the directivity and the frequency characteristic. [0008] An area on the back side of the back plate 14, which is surrounded by an inner circumference of the case 12, is a hollow space 18. Together with the through holes 15 and the acoustic resistors 16, the hollow space 18 forms a phase-shift circuit to obtain directivity. The frequency dependence of the unidirectional microphone unit controls the vibration of the diaphragm 13 by the acoustic resistors 16. If a resistance value of the acoustic resistors 16 is increased, the directivity is decreased to finally provide no directivity. [0009] In a DC-bias capacitor microphone, a DC-bias voltage is applied through a high resistance between a vibrating membrane and a back plate. In the case shown in FIG. 8, a DC power source for biasing is connected between the diaphragm 13 and the outer casing 11 (not shown) so that the outer casing 11 and the case 12 function as the high resistance. [0010] By a change in capacitance of the microphone unit shown in FIG. 8, a change in voltage occurred between both ends of the high resistance (that is, between the outer casing 11 and the terminal 14aa) is obtained as an electric signal. [0011] Conventionally, as described in Japanese Patent Application Publication No. Sho 60-22897, a so-called MS microphone, which uses a unidirectional microphone unit and a bidirectional microphone unit to obtain a stereophonic sound, has been proposed. SUMMARY OF THE INVENTION [0012] If the diaphragm 13 of the unidirectional microphone unit shown in FIG. 8 is oriented toward a sound source situated on the front, sound on the rear side (behind the microphone unit) is cancelled by the offset between sound entering the microphone unit through the acoustic resistors 16 and the through holes 15 of the rear plate 12R and sound taking a detour from the back to the front to be introduced through the diaphragm 13. [0013] However, the unidirectional microphone unit has a so-called proximity effect; when a sound source located behind is close to the microphone unit, a bass sound is enhanced in a sound coming from the sound source. [0014] Since the MS microphone described in Japanese Patent Application Publication No. Sho 60-22897 includes the unidirectional microphone unit, the microphone unit is difficult to have a broad frequency characteristic to a bass sound range as in the case of a non-directional microphone unit, due to a structural characteristic of the unidirectional microphone unit. Furthermore, a directional characteristic in the bass sound range is inferior to that of a midrange. [0015] The present invention is devised in view of the above circumstances and aims to provide a microphone capable of providing a two-channel stereo output and a four-channel stereo output with favorable directivity and frequency characteristic. [0016] A microphone according to an embodiment of the present invention has: [0017] (1) a first bidirectional microphone unit formed by connecting two unidirectional microphone units, each having a vibrating section on a front side, back to back; and a second bidirectional microphone unit formed by connecting two unidirectional microphone units, each having a vibrating section on a front side, back to back, the second bidirectional microphone unit being arranged so that its directional axis is shifted by 90 degrees with respect to that of the first bidirectional microphone unit. [0018] In the unidirectional microphone, when a front side having a vibrating section (a diaphragm, a vibrating membrane or the like) is oriented toward a sound source, a rear sound is cancelled by the offset between a sound entering the microphone from the back and a sound taking a detour to enter from the front. As a result, the unidirectional microphone has unidirectionality to capture only a front sound. [0019] The unidirectional microphone has a so-called proximity effect; when a sound source situated behind is close to the microphone unit, a bass sound is enhanced in a sound coming from the back. In the bidirectional microphone unit according to an embodiment of the present invention, however, among the unidirectional microphones connected to each other back to back, the vibrating section of one of the unidirectional microphones is situated on the rear face side of the other unidirectional microphone and the vibrating section of the other unidirectional microphone is situated on the rear face side of one unidirectional microphone. Therefore, each of the vibrating sections acts as a compliance for correcting the proximity effect (an acoustic compliance; cm.sup.3/.mu.bar) to keep the unidirectionality even in a relatively low frequency. [0020] Since the compliance has an increasing reactance as a frequency becomes lower, an acoustic pressure of an acoustic wave introduced from the back of the microphone becomes gradually smaller. Specifically, the characteristic of the microphone becomes closer to that of a non-directional microphone whose back is closed. Therefore, a frequency characteristic on the front side becomes flat to a bass sound range. As a result, favorable directivity and a broad frequency characteristic to a bass sound range can be obtained, which are not affected by a difference in frequency. [0021] (2) The first bidirectional microphone unit inputs an acoustic signal corresponding to a front and rear channel, the second bidirectional microphone unit inputs an acoustic signal corresponding to a left and right channel, and the microphone includes a two-channel signal circuit for generating and outputting a two-channel acoustic signal of front left and front right channel, formed from the acoustic signal corresponding to the front channel output from the first bidirectional microphone unit and from the acoustic signal corresponding to the left and right channel output from the second bidirectional microphone unit. [0022] With the first and the second bidirectional microphone units and the two-channel signal circuit, a two-channel stereo microphone having favorable directivity that is not varied by a difference in frequency can be configured. Continue reading about Microphone... Full patent description for Microphone Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Microphone patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. Start now! - Receive info on patent apps like Microphone or other areas of interest. ### Previous Patent Application: Gigbox: a music mini-studio Next Patent Application: Biasing circuit for sound source amplifier Industry Class: Electrical audio signal processing systems and devices ### FreshPatents.com Support Thank you for viewing the Microphone patent info. IP-related news and info Results in 0.2621 seconds Other interesting Feshpatents.com categories: Medical: Surgery , Surgery(2) , Surgery(3) , Drug , Drug(2) , Prosthesis , Dentistry 174 |
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